Interfaces to connect a storage system to a computer are mainly classified into two types.
First, a block input/output (I/O) interface is used to conduct I/O operations between a storage system and a computer using a unit of blocks as a data control unit in the storage system. The block I/O interface includes a Fibre Channel, a small computer systems interface (SCSI), and the like.
A network in which a plurality of storage systems having a block I/O interface are connected to a plurality of computers is called a storage area network (SAN). SAN includes a Fibre Channel in many cases. JP-A-10-333839 describes an example of a storage system connected to a storage area network using a Fibre Channel.
Second, a file I/O interface is used to conduct I/O operations between a storage system and a computer using a unit of files recognized by an application program executed by the computer. The file I/O interfaces uses, in many cases, a protocol of a network file system employed by a file server of the prior art.
Particularly, an apparatus in which functions of the file server customized for the storage system are combined with the storage system is called a network attached storage (NAS). The NAS is directly connected to a local area network (LAN) and the like.
In a storage are network (SAN), the computer is connected to the storage system via a high-speed network exclusively constructed for the storage system, the network being separated from a network used to exchange messages between computers. Therefore, in the SAN higher speed data communication can be executed when compared with the NAS connected via the LAN to the computer. Since the SAN adopts the block I/O interface, overhead of protocol processing is lowered when compared with the NAS, and hence a high-speed response can be achieved.
However, since the SAN requires a network system dedicated to the storage system, installation of the SAN requires a higher cost. Therefore, the SAN is primarily used in a backbone system of an enterprise to construct a database in many cases.
On the other hand, since the NAS can directly use an existing LAN, the installation cost thereof is lowered and the installation becomes easier. The NAS uses a standardized network file system and hence the NAS user can manage data in the unit of general files. Therefore, data can be easily managed and files can be easily shared among a plurality of computers.
However, the NAS communicates data with computers via the LAN also used for communications between the computers. There exists risk that the load of the LAN is increased. Since the protocol processing used in the network file system has high overhead and hence the response time becomes longer as compared with the SAN. Therefore, the NAS is primarily used in a file management or control system of an enterprise for application to manage web contents, data files of computer aided design, and the like in many cases.
As above, the NAS and the SAN are complementary to each other and are applied to mutually different fields. Therefore, the NAS and the SAN are respectively used in appropriate fields.
For each computer to use a necessary amount of storage capacity of the storage system according to necessity, there exists a technique called a storage pool in which each resource (to be referred to as a device hereinbelow) of the storage system can be easily set and can be easily allocated to each computer. JP-A-2001-142648 describes an example of the storage pool.